lomnitz-salvador-rept.doc - Submitted to Seismological...

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Submitted to Seismological Research Letters El Salvador 2001: Earthquake disaster and disaster preparedness in a tropical volcanic environment Cinna Lomnitz and Sergio Rodríguez Elizararrás Universidad Nacional Autónoma de México We visited El Salvador two weeks after the disastrous earthquake of 13 January 2001 (Mw=7.6) at the request of the Ambassador of El Salvador in Mexico. Mexico is close to El Salvador in many ways, and one of us had studied an earlier earthquake disaster in this country (Lomnitz and Schultz, 1966). One result is the present report of our fact-finding emergency mission. We thank the government of El Salvador for timely and effective assistance and hospitality. It is a pleasure to acknowledge the valuable comments of José Luis Chávez and Franz Sauter in the course of field work. The earthquake The main earthquake occurred on Saturday, 13 January 2001 at 11:33 a.m. local time off the south coast of El Salvador at 12.83 0 N, 88.79 0 W with a focal depth of around 40 km. A second major shock (Mw=6.6) occurred on February 13, 2001. There were over 1,000 deaths, mostly in landslides. The focal mechanism of the first event suggested intraplate normal faulting in the subducting Cocos Plate. The trend of the fault was nearly parallel to the coast. The magnitude was Mw=7.6. There were reports of a minor tsunami. Over a thousand aftershocks occurred in a nearly circular area with a diameter of about 50 km (Fig. 1). The rate of occurrence of aftershocks decayed roughly according to Omori’s Law. The second major shock occurred inland from the first one, near the town of San Vicente: it had a shallow focus and a strike-slip mechanism. The capital city of San Salvador is located more than 100 km from the epicenter. Accelerations of 0.3 g to 0.6 g were recorded in the city, and substantial seismic damage to housing was feared. We found, however, that the seismic behavior of structures in San Salvador--a rapidly growing city of nearly 2 million--had been excellent. Non- structural did damage did exist but was not much in evidence: we had to look for it. The Central American University, a private college, had obtained a good set of strong-motion records from their network of nine digital
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stations, most of them in San Salvador and nearby localities. They recorded peak horizontal ground accelerations of up to 0.89g at the port of La Libertad, and up to 0.59g at inland locations. The frequencies seemed high, perhaps because of the focal depth. We were puzzled that no more substantial structural damage had occurred in spite of the high intensity values. Major loss of life occurred in a landslide in Las Colinas, a middle- class residential development in the Santa Tecla district of greater San Salvador. The scar of the landslide was relatively shallow and rectangular in shape (Fig. 2). During the strong ground motion, the hillside flowed down with a hissing noise; the homes in the path of the landslide were destroyed and about 400 people were killed. The homes on either side of the landslide were evacuated for fear of further slides,
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  • Fall '18
  • Don Reed
  • El Salvador

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